Kernel panic

A kernel panic is an action taken by an operating system upon detecting an internal fatal error from which it cannot safely recover; the term is largely specific to Unix and Unix-like systems.

The kernel routines that handle panics (in AT&T-derived and BSD Unix source code, a routine known as panic()) are generally designed to output an error message to the console, dump an image of kernel memory to disk for post-mortem debugging and then either wait for the system to be manually rebooted, or initiate an automatic reboot. The information provided is of highly technical nature and aims to assist a system administrator or software developer in diagnosing the problem.

Attempts by the operating system to read an invalid or non-permitted memory address are a common source of kernel panics. A panic may also occur as a result of a hardware failure or a bug in the operating system. While technically often the operating system could continue operation, after memory violations have occurred the system is in an unstable state. Rather than risk security breaches and data corruption, the operating system stops to prevent further damage and facilitate diagnosis of the error.

The kernel panic was introduced in an early version of Unix and demonstrated a major difference between the design philosophies of Unix and its predecessor Multics. Multics developer Tom van Vleck recalls a discussion of this change with Unix developer Dennis Ritchie:

The original panic() function was essentially unchanged from Fifth Edition UNIX to the VAX-based UNIX 32V and output only an error message with no other information, then dropped the system into an endless idle loop. As the Unix codebase was enhanced, the panic() function was also enhanced to dump various forms of debugging information to the console.

See also

* Bug check
* Screens of death

References

External links

* [http://opensolaris.org/os/community/documentation/files/book.pdf The Solaris Operating System on x86 Platforms: Crashdump Analysis Operating System Internals]
* [http://www.amazon.com/gp/product/0131493868 "Panic! Unix System Crash Dump Analysis" (SunSoft Press / Prentice Hall book by Chris Drake & Kimberley Brown]
* The file [http://minnie.tuhs.org/UnixTree/V6/usr/sys/ken/prf.c.html prf.c] from Version 6 Unix and the Lions Book, containing the "panic()" routine as implemented on early Unix systems (will not compile with modern C compilers)
* Kernel panic source code examples from [http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/os/panic.c OpenSolaris] , [http://darwinsource.opendarwin.org/10.4.2/xnu-792.2.4/osfmk/kern/debug.c Darwin/Mac OS X] , [http://www.eng.mu.edu/corlissg/MSCS207.1998/Minix_tree/S/sys%20src%20kernel%20main.c.html#130 Minix] , and [http://developer.osdl.org/ogasawara/kernel_gcov/kernel/panic.c.gcov.html Linux]